ST7261 datasheet(47/80 Pages) STMICROELECTRONICS

47 / 80 page

ST7261

47/80

INSTRUCTION SET OVERVIEW (Cont’d)

10.2 INSTRUCTION GROUPS

The ST7 family devices use an Instruction Set

consisting of 63 instructions. The instructions may

be subdivided into 13 main groups as illustrated in

the following table:

Using a pre-byte

The instructions are described with one to four op-

codes.

In order to extend the number of available op-

codes for an 8-bit CPU (256 opcodes), three differ-

ent prebyte opcodes are defined. These prebytes

modify the meaning of the instruction they pre-

cede.

The whole instruction becomes:

PC-2

End of previous instruction

PC-1

Prebyte

opcode

PC+1

Additional word (0 to 2) according

to the number of bytes required to compute the ef-

fective address

These prebytes enable instruction in Y as well as

indirect addressing modes to be implemented.

They precede the opcode of the instruction in X or

the instruction using direct addressing mode. The

prebytes are:

PDY 90

Replace an X based instruction

using immediate, direct, indexed, or inherent ad-

dressing mode by a Y one.

PIX 92

Replace an instruction using di-

rect, direct bit, or direct relative addressing mode

to an instruction using the corresponding indirect

addressing mode.

It also changes an instruction using X indexed ad-

dressing mode to an instruction using indirect X in-

dexed addressing mode.

PIY 91

Replace an instruction using X in-

direct indexed addressing mode by a Y one.

Load and Transfer

CLR

Stack operation

PUSH

POP

RSP

Increment/Decrement

INC

DEC

Compare and Tests

TNZ

BCP

Logical operations

AND

XOR

CPL

NEG

Bit Operation

BSET

BRES

Conditional Bit Test and Branch

BTJT

BTJF

Arithmetic operations

ADC

ADD

SUB

SBC

MUL

Shift and Rotates

SLL

SRL

SRA

RLC

RRC

SWAP

SLA

Unconditional Jump or Call

JRA

JRT

JRF

CALL

CALLR

NOP

RET

Conditional Branch

JRxx

Interruption management

TRAP

WFI

HALT

IRET

Condition Code Flag modification

SIM

RIM

SCF

RCF

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